A gear variable speed mechanism that varies speed by gear ratio has been known in the art of a power transmission apparatus. Moreover, a CVT (Continuously Variable Transmission) is known as an apparatus that continuously varies speed of the rotation of a power device without steps (refer to patent document 1).
In CVT, two pulleys, at an output end and a driving end, respectively, are connected by a steel belt attached to a top. It is characterized in that the width of the two pulleys is changed hydraulically and the diameter of the pulley increases as its width increases and the diameter decreases as its width deceases. Thus, the rotation of the driving end is varied and transmitted to the output end. Patent document 1: Patent Publication No. 2001-518171.